The present invention relates to a plating method and apparatus for plating an object, and particularly to a plating method and apparatus for forming a plating film in the wiring channels and plugs formed in a substrate such as a semiconductor wafer or opening portions in the resist formed on the surface of the substrate.
FIG. 1 shows the construction of a conventional plating apparatus. As shown in the drawing, the plating apparatus includes a plating bath 100. The plating bath 100 is provided with a main body 101 accommodating a plating solution Q2, and a collecting vessel 102 for collecting the plating solution Q2 that overflows from the main body 101. A pump 103 transfers the plating solution Q2 collected in the collecting vessel 102 to a temperature regulator 104. The temperature regulator 104 regulates the plating solution Q2 to a predetermined temperature appropriate for plating. A filter 105 is provided for removing particles and the like from the plating solution Q2 as the solution is supplied to the main body 101. A flow meter 106 is provided for measuring the circulating flow of the plating solution.
With the construction described above, a substrate W such as a semiconductor wafer is retained in a retainer 108 within the main body 101, while an anode 107 is disposed also in the main body 101 and opposing the substrate W. A power source 109 supplies an electrical current between the substrate W and the anode 107 in order to plate the substrate W. When performing electroless plating, the plating bath 100 is not provided with the power source 109 or the anode 107. The plating process includes immersing the substrate W into the plating solution Q2.
When forming a plating film in fine channels or plugs for wiring formed in the substrate W or in opening portions of resist having poor wettability, sometimes the plating solution or preprocess solution cannot enter these fine openings, leaving air bubbles in the same. These bubbles can cause defects or omissions in the plating film.
In order to prevent such defects or omissions in the plating, a surface active agent has been added to the plating solution in conventional methods with the aim of lowering the surface tension of the plating solution to allow plating solution to enter the fine channels and plugs of the substrate and opening portions in the resist. However, lowering the surface tension of the plating solution increases the tendency of the air bubbles to generate on the surface of the solution during circulation. Further, adding new surface active agent to the plating solution causes abnormalities to occur in the plating deposition and increases the amount of organic matter taken in by the plating film. Hence, this method can have an adverse effect on the properties of the plating film.
In view of the foregoing, it is an object of the present invention to provide a plating method and apparatus capable of introducing plating solution into the fine channels and holes formed in a substrate without needing to add a surface active agent to the plating solution and capable of forming a high-quality plating film having no defects or omissions.
To achieve the above object, there is provided a plating method for performing electrolytic or electroless plating of an object using a plating solution, which comprises: conducting a plating operation after or while deaerating dissolved gas from the plating solution; and/or conducting a preprocessing operation using a preprocessing solution after or while deaerating dissolved gas from preprocessing solution and subsequently conducting the plating operation.
By deaerating the plating solution before or while performing the plating process as described above, air bubbles existing in the fine channels and plugs formed in the object to be plated and in opening portions of the resist coated on the surface of the object are absorbed into the deaerated plating solution, thereby enabling plating solution to enter the fine channels and holes and produce a plating film without defects or omissions. Removing dissolved gas from the plating solution prevents reactions by the dissolved gas as the plating solution is circulated, thereby achieving a stable plating environment that restrains side reactions that can degrade the quality of the plating solution.
By deaerating the preprocessing solution as described above, air bubbles existing in the fine channels and plugs formed in the object to be plated are absorbed into the deaerated preprocessing solution when the object is immersed therein, thereby enabling preprocessing solution to enter the fine channels and holes. When the object to be plated is subsequently immersed in the plating solution, preprocessing solution existing in the fine channels and holes is replaced by plating solution, thereby enabling plating solution to enter the fine channels and holes and produce a plating film without defects or omissions.
It is desirable that the concentration of dissolved gas in either one or both of the plating solution and the preprocessing solution be regulated between 4 ppm and 1 ppb during the plating process. A stable plating process can be achieved by monitoring the concentration of dissolved gas in the plating solution passing through a plating solution circulating path or the preprocessing solution passing through a preprocessing solution circulating path, and by regulating the amount of dissolved gas in the solutions based on the data obtained.